This project will investigate the hormonal regulation of the biosynthesis of lamellar body material, the precursor form of pulmonary surfactant. The animal model utilized will be the organ culture of fetal rabbit lung. This tissue will be maintained in serum-free medium with no added hormones, or with the addition of cortisol, thyroxine, or both in combination. These hormones have been chosen because they have received the most attention as regulators of lamellar body production in the fetal lung. The effects of hormone treatment will be assessed first by quantitative measurement of the lamellar body material produced during the culture period. Secondly, compositional changes will be investigated. These will be assessed by measurement of phospholipid to protein ratios, phosphatidate phosphohydrolase activity, phosphatidylcholine fatty acid profiles, and surface activity. Finally, hormonal regulation will be assessed by measurement of changes in the turnover time of the intracellular lamellar body pool. Emphasis is given to the identification of lamellar body polypeptides because they may represent unambiguous chemical markers of lamellar body production. This investigation will also serve to develop methodologies for studying the effects of other regulators of type II cell metaboism, including regulation by the surrounding mesenchymal cells.